Time-lapse cinematography, resulting in an acceleration of motion upon reproduction, is used for trick films and also for the study of slowly progressing phenomena such as, for example, the growth of a plant. Moreover, poor illumination sometimes makes it necessary to prolong the exposure time of individual film frames in situations in which the resulting apparent acceleration can be tolerated, as during the filming of scenery with little or no motion. The latter situation also exists where a film camera is used for the production of slides or other still pictures to be copied from the individual frames.
In operating a camera with such an extended shutter cycle, it is necessary to select two separate but interrelated parameters, namely the recurrence period of shutter closure and the exposure interval which generally should be less than that recurrence period. Since the exposure interval depends upon the luminous intensity of the object or scene to be photographed, this interval should be automatically adjustable with the aid of a photometric device which may modify the setting of an electronic pulse counter steppable by a square-wave oscillator. Conventional systems utilizing such pulse generators may be built into the camera or connected to it as a separate attachment.